Photomask blank manufacturing method and photomask manufacturing method

Abstract

A thin film made of a material containing a metal and silicon is formed on a light-transmissive substrate. Then, a treatment is performed to modify a main surface of the thin film in advance so that when exposure light having a wavelength of 200 nm or less is accumulatively irradiated on a thin film pattern of a photomask to be produced by patterning the thin film, the transfer characteristic of the thin film pattern does not change more than a predetermined degree. This treatment is performed by carrying out, for example, a heat treatment in an atmosphere containing oxygen at 450° C. to 900° C.

Description

[0001]This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-335663, filed on Dec. 29, 2008, the disclosure of which is incorporated herein in its entirety by reference.TECHNICAL FIELD[0002]This invention relates to methods of manufacturing a photomask blank and a photomask and, in particular, relates to a method of manufacturing a photomask blank for use in the manufacture of a photomask to be suitably used in an exposure apparatus using exposure light having a short wavelength of 200 nm or less and to a method of manufacturing such a photomask.BACKGROUND ART[0003]Generally, fine pattern formation is carried out by photolithography in the manufacture of a semiconductor device. A number of substrates called photomasks are normally used for such fine pattern formation. The photomask comprises generally a light-transmissive glass substrate having thereon a fine pattern made of a metal thin film or the like. The photolithography is u...

AI Technical Summary

Benefits of technology

The present invention aims to provide a method for manufacturing a photomask blank that can improve the light fastness of a thin film used for forming a transfer pattern, thereby improving the lifetime of the photomask. The invention addresses the issue of mask degradation caused by repeated use of the photomask and the need for a longer lifetime of the photomask. The method involves heat treatment of the thin film to form a modified layer that contributes to the changes in transmittance, phase difference, and line width of the photomask. By reducing the oxidation rate of the thin film, the formation and enlargement of the modified layer can be suppressed, leading to improved light fastness of the photomask and reduced pattern deformation.

Problems solved by technology

Following the reduction in exposure light wavelength in recent years, however, mask degradation due to repeated use of a photomask has become notable.

In the case of the phase shift mask, such changes in transmittance and phase difference are serious problems that affect the mask performance.

If the change in transmittance becomes large, the transfer accuracy is degraded, while if the change in phase difference becomes large, the phase shift effect at the pattern boundaries is difficult to obtain so that the contrast at the pattern boundaries is lowered and thus the resolution is significantly reduced.

Further, the change in line width degrades the CD accuracy of the photomask and finally degrades the CD accuracy of a pattern-transferred wafer.

Conventionally, for example, when haze is generated, cleaning is carried out for removing the haze, but a film loss (dissolution) due to the cleaning cannot be avoided and thus, roughly, the number of times of cleaning determines the mask lifetime.

However, since the number of times of cleaning is reduced due to an improvement to haze in recent years, the period of time of repeated use of a photomask is prolonged and thus the exposure time is prolonged correspondingly, and therefore, a problem of light fastness particularly to short-wavelength light such as ArF excimer laser light has been newly actualized.

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